Apparatus and method for generating transmission and reception local oscillation signals in a mobile terminal

ABSTRACT

There is provided an apparatus for generating a transmission of local oscillation signals and a reception of local oscillation signals in a mobile terminal. The apparatus includes: a first phase locked loop (PLL) block configured to generate a transmission local oscillation signal; a second PLL block configured to generate a reception local oscillation signal; and a controller configured to control the first PLL block to operate before a minimum time period required for the first PLL block to lock up from a start point of a transmission burst period and the second PLL block to operate before a minimum time period required for the second PLL block to lock up from a start point of a reception burst period.

PRIORITY

[0001] This application claims priority to an application entitled“Apparatus and Method for Generating Transmission and Reception LocalOscillation Signals in Mobile Terminal” filed in the Korean IndustrialProperty Office on Oct. 19, 2000 and assigned Serial No. 2000-61478, thecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a mobile terminal, andin particular, to an apparatus and method for generating transmissionand reception local oscillation signals.

[0004] 2. Description of the Related Art

[0005] In a mobile terminal, a local oscillation signal for transmission(TX local oscillation signal) is used to upconvert the frequency of atransmission signal, whereas a local oscillation signal for reception(RX local oscillation signal) is used to downconvert the frequency of areceived signal. The TX and RX local oscillation signals are generatedby a PLL (Phase Locked Loop) block and provided to a radio transmitterand a radio receiver, respectively.

[0006] In a conventional TDD (Time Division Duplex) mobile terminal, aTX local oscillation signal and an RX local oscillation signal areselectively provided by a PLL block 8 as shown in FIG. 1. The PLL block8 synchronizes the frequency and phase of its output signal to those ofa reference signal or an input signal.

[0007] Referring to FIG. 1, the PLL block 8 is comprised of a frequencysynthesizer 2, a low pass filter (LPF) 4, and a voltage controlledoscillator (VCO) 6. A controller (not shown) feeds an enable signal EN,data DT, a clock signal CLK to the frequency synthesizer 2 of the PLLblock 8, so that the PLL block 8 may selectively provide: a TX localoscillation signal (TX LO) to a radio transmitter in a transmissionmode, and an RX local oscillation signal (RX LO), to a radio receiver ina reception mode. The data DT controls values for the TX and RX localoscillation signals. The frequency synthesizer 2 receives the data DT,in an active logic low state of the enable signal EN, in response to theclock signal CLK. The frequency synthesizer 2 generates a signal with avery stable frequency, by synthesizing a signal of a reference signalsource received from a reference signal generator, based on the data DT.The LPF 4 filters the signal received from the frequency synthesizer 2and provides a voltage value corresponding to the filtered signal to theVCO 6. The VCO 6 generates a signal with an oscillation frequencycorresponding to the voltage value, that is, TX LO or RX LO. TX LO andRX LO are provided to the radio transmitter and the radio receiver,respectively. Then the TX and RX oscillation signals are fed back to thefrequency synthesizer 2 at the same time.

[0008] It is possible to selectively generate a TX local oscillationsignal and an RX local oscillation signal using the single PLL block 8in the conventional TDD mobile terminal for the following reason. TheTDD mobile terminal has a frame structure as shown in FIG. 2. Referringto FIG. 2, the frame is a GSM (Global System for Mobiletelecommunication) TDMA (Time Division Multiple Access) frame. Each GSMTDMA frame is 4.615 ms in duration and has a gap of about 1.154 msbetween a TX burst period and an RX burst period. The 1.154 ms gap issufficient for the PLL block 8 to secure a time required to y switchfrequencies from TX LO, and RX LO, local oscillation signals(hereinafter, referred to as PLL lock-up time” or “frequency switchingtime”). Therefore, the TDD mobile terminal can generate TX LO in atransmission mode and RX LO in a reception mode by use of the single PLLblock 8.

[0009] However, a propagation delay that occurs in a multi-time slotmode, between a mobile terminal, or between a mobile terminal and a basestation must be considered when multi-slot standards are supported as inHSCSD (High-Speed Circuit Switched Data) and GRS (General RadioService), or a satellite-based TDD scheme is employed.

[0010] The conventional mobile communication system does not need ashort PLL lock-up time because it mainly provides voice transmission. Onthe contrary, future mobile communication systems will be configured toadditionally provide transmission of pictures and data communication.For the resulting use of multi-time slots in a TDMA frame, the PLLlock-up time should be reduced. However, the conventional method shownin FIG. 1 has limitations in reducing the PLL lock-up time because asthe PLL lock-up time decreases, the phase noise performance of the PLLblock deteriorates.

[0011] Therefore, there exists a need for an apparatus and a method thatprovides a shorter frequency switching time, or a shorter PLL lock-uptime, which allows the PLL block to provide a transmission of picturesand data communication.

SUMMARY OF THE INVENTION

[0012] It is, therefore, an object of the present invention to providean apparatus for generating local oscillation signals for transmissionand reception in a mobile terminal that exchanges voice, images, anddata.

[0013] It is another object of the present invention to provide a methodfor switching frequencies between a transmission of a local oscillationsignal and a reception of a second local oscillation signal even thoughthe gap between a transmission burst period and a reception burst periodis short in a mobile terminal.

[0014] To achieve the above objects, there is provided an apparatus forgenerating a transmission of a local oscillation signal and a receptionof a second local oscillation signal in a mobile terminal, the apparatuscomprising: a first phase locked loop (PLL) block configured to generatea transmission of a local oscillation signal; a second PLL blockconfigured to generate a reception of a local oscillation signal; and acontroller configured to control the first PLL block to operate before aminimum time period required for the first PLL block to lock up from astart point of a transmission burst period and the second PLL block tooperate before a minimum time period required for the second PLL blockto lock up from a start point of a reception burst period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0016]FIG. 1 is a block diagram of a PLL block utilized to generate a TXlocal oscillation signal and an RX local oscillation signal in aconventional mobile terminal;

[0017]FIG. 2 illustrates the structure of a typical GSM TDMA frame;

[0018]FIG. 3 is a block diagram of a typical mobile terminal;

[0019]FIG. 4 is a block diagram of PLL blocks utilized to generate a TXlocal oscillation signal and an RX local oscillation signal, accordingto an embodiment of the present invention; and

[0020]FIG. 5 is an operational timing diagram, according to theembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

[0022]FIG. 3 is a block diagram of a typical mobile terminal and FIG. 4is a block diagram of PLL blocks utilized to generate a TX localoscillation frequency and an RX local oscillation frequency, accordingto an embodiment of the present invention.

[0023] Referring to FIG. 3, there is a typical mobile terminal. Themobile terminal is comprised of a controller 100, a memory 102, a keypad104, a display 106, an antenna 108, a RF (Radio Frequency) Module 110, aBaseband Processor 112, a CODEC (Coder-Decoder) 114, an amplifier 116, amicrophone 118, a speaker 120, a ringer 122 and a vibrator 124.Controller 100 is connected to: memory 102, keypad 104, display 106, RF(Radio Frequency) module 110, baseband processor 112, CODEC(Coder-Decoder) 114 AND amplifier 16. In addition, controller 100processes a normal telephone call or data communication and processes avoice signal and data for wireless Internet access, according to acorresponding protocol. Further, controller 100, instructs eachcomponent of the mobile terminal. The memory 102 includes a ROM (ReadOnly Memory), a flash memory, and a RAM (Random Access Memory). The ROMstores operation and control programs and data for the controller 100.The RAM provides a working memory for the controller 100. The flashmemory provides an area for storing updatable data.

[0024] The keypad 104 has a plurality of keys including digit keys andprovides a key input signal to the controller 100. The display 106usually includes an LCD (Liquid Crystal Display), which displaysinformation under the control of the controller 100. The RF module 110receives an RF signal from a base station via an antenna 108, thenconverts the received RF signal to an IF (Intermediate Frequency)signal, and outputs the IF signal to the baseband processor 112. The RFmodule 110 also converts an IF signal received from the basebandprocessor 112 and transmits the RF signal to the base station. Thebaseband processor 112 is a baseband analog ASIC (BBA) that interfacesthe controller 100 to the RF module 110. The baseband processor 112converts a digital baseband signal received from the controller 100 toan analog IF signal. Then the baseband processor feeds the analog IFsignal to the RF module 110. Baseband processor 112 also converts an RFsignal to an analog IF signal received from the RF module 110 to adigital baseband signal, then feeds the digital baseband signal to thecontroller 100. The CODEC 114 is connected to a microphone 118 and aspeaker 120 through amplifier 116. The CODEC 114 PCM (Pulse CodeModulation)-encodes a voice signal received from the microphone 118,then outputs the voice data to the controller 100. CODEC 114 PCM-decodesvoice data received from the controller 100, then outputs the voicesignal to the speaker 120 via the amplifier 116. The amplifier 116amplifies a received voice signal or a voice signal to be transmitted tothe speaker 120 and adjusts the volume of the speaker 120 and the gainof the microphone 118 while under the control of the controller 100. Aringer 122 generates a bell sound under the control of the controller100, and a vibrator 124, under the control of the controller 100,generates vibrations.

[0025] The RF module 110 includes a first PLL block 18, and a second PLLblock 28 as shown in FIG. 4, according to the embodiment of the presentinvention. The controller 100 controls the PLL blocks 18 and 28.

[0026] Along with the recent trend of transmission of pictures and data,as well as voice transmission, multi-time slots are used in a dataframe. Therefore, a gap between a transmission burst period and areception burst period is narrowed. This implies that it is difficult tosecure a PLL lock-up time required for a PLL to switch a TX localoscillation signal to an RX local oscillation signal. Unless the PLLlock-up time is secured, phase noise characteristics are deteriorated.

[0027] Since there is a limit in reducing the PLL lock-up time by use ofa single PLL, the two PLL blocks 18 and 28 are provided in theembodiment of the present invention. By controlling the PLL blocks 18and 28 with the controller 100, the PLL lock-up time is definitelysecured.

[0028] Referring to FIG. 4, the first PLL block 18 generates a TX localoscillation signal to a radio transmitter and the second PLL block 28generates an RX local oscillation signal to a radio receiver. Thecontroller 100 instructs the first PLL block 18 to operate in a timeshorter than a minimum time required for the PLL to lock up block 18from the starting point of a transmission burst period. In addition,controller 100 instructs second PLL block 28 to operate in a timeshorter than a minimum time required for the PLL block 18 to lock upfrom the starting point of a reception burst period.

[0029] A first frequency synthesizer 12, a first LPF 14, and a first VCO16 in the first PLL block 18 and a second frequency synthesizer 22, asecond LPF 24, and a second VCO 26 in the second PLL block 28 operate inthe same manner as their counterparts in FIG. 1. Thus, the components ofthe first and second PLL blocks 18 and 28 are not described here.

[0030] The controller 100 applies a data DT and a clock signal CLK toboth the first frequency synthesizer 12 and the second frequencysynthesizer 22, according to the embodiment of the present invention.The controller 100 applies a transmission enable signal EN_TX to thefirst frequency synthesizer 12 and a reception enable signal EN_RX tothe second frequency synthesizer 22.

[0031]FIG. 5 is an operational timing diagram of the transmission enablesignal EN_TX, the reception enable signal EN_RX, the clock signal CLK,and the data DT provided by the controller 100, according to theembodiment of the present invention.

[0032] The operation of the PLL blocks, according to the embodiment ofthe present invention, will be described in detail referring to FIGS. 3,4, and 5.

[0033] As shown in FIG. 5, the narrowest gap between a transmissionburst period 30 and a reception burst period 32 by 9 symbols, is about500 μsec. The 500 μsec gap is too short to be a PLL lock-up time.Therefore, the controller 100 controls the PLL blocks 18 and 28 to havea sufficient PLL lock-up time according to the embodiment of the presentinvention.

[0034] To do so, the controller 100 instructs the first PLL block 18 tooperate before a minimum time P1 required for the first PLL block 18 tolock up from the start point, St, of the transmission burst period 30,that is, at a time point t1. Specifically, the controller 100 shifts thetransmission enable signal EN_TX to an active low state, at the timepoint t1, and provides the clock signal CLK. The data DT correspondingto the frequency of a TX local oscillation signal, TX LO, is provided tothe first PLL block 18 for a period when the transmission enable signalEN_TX is in the active logic low state. As a result, the first PLL block18 generates the TX LO, in response to the data DT and the clock signalCLK. Even for the minimum time P1 required for the first PLL block 18 tolock up, the first PLL block 18 generates TX LO and provides it to theradio transmitter of the RF module 110. Since the radio transmitter isdisabled in a non-transmission burst period, the generation of the TX LOfor the time period P1 has no influence on the operation of the mobileterminal.

[0035] According to another embodiment of the present invention, thecontroller 100 instructs the first PLL block 18 to operate before theend point of the reception burst period 32, for example, near the timepoint t1.

[0036] To operate the second PLL block 28 with a sufficient PLL lock-uptime, the controller 100 instructs the second PLL block 28 to operatebefore a minimum time P2 required for the second PLL block 28 to lock upfrom the starting point, Sr, of the reception burst period 32, that is,at a time point t2. Specifically, the controller 100 shifts thereception enable signal EN_RX to an active low state at the time pointt2 and provides the clock signal CLK. The data DT corresponds to thefrequency of an RX local oscillation signal RX LO is provided to thesecond PLL block 28 for a period when the reception enable signal EN_RXis in the active logic low state. As a result, the second PLL block 28generates RX LO in response to the data DT and the clock signal CLK.Even for the minimum time P2 required for the second PLL block 28 tolock up, the second PLL block 28 generates RX LO and provides it to theradio receiver of the RF module 110. Since the radio receiver isdisabled in a non-reception burst period, the generation of RX LO forthe time period P2 has no influence on the operation of the mobileterminal.

[0037] It is further contemplated as another embodiment of the presentinvention that the controller 100 instructs the second PLL block 28 tooperate before the end point of the transmission burst period 30, forexample, in the vicinity of the time point t2.

[0038] As described above, the gap (e.g., 500 μsec) between thetransmission burst period and the reception burst period and some time(e.g., α seconds) before the gap period are given as a PLL lock-up timeso that a PLL has a sufficient lock-up time in the present invention.Hence, without increasing the PLL lock-up time, PLL phase noisecharacteristics can be optimized.

[0039] Table 1 shows the relationship between a PLL lock-up time andphase noise as measured in a mobile terminal for communication of voice,pictures, and data. TABLE 1 test condition unit phase noise frequencyoffset 1.0 −70 −71.0 dBc/Hz 5.0 −66.0 −69.0 12.5 −71.0 −78.0 25.0 −80.0−88.0 50.0 −90.0 −98.0 100 −101.0 −109.0 lock-up time 500 800 μsec

[0040] As noted from Table 1, phase noise is very different, accordingto lock-up time 500 μsec and 800 μsec under the same conditions. It canbe concluded that application of the present invention stabilizes theoperation of a PLL block when phase noise characteristics do not come upto a specification, or a margin between the phase noise characteristicsand the specification is not enough.

[0041] In accordance with the present invention as described above, aPLL can be lock up more steadfastly in a TDD mobile terminal, especiallya mobile terminal requiring a short PLL lock-up time, and the mobileterminal can be designed such that the phase noise characteristics of aPLL block are reflected. While the conventional PLL scheme is limited inincreasing a PLL lock-up time to satisfy a given phase noisespecification due to the relation between the PLL lock-up time and phasenoise, the PLL lock-up time can be increased without influencing phasenoise characteristics.

[0042] While the invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An apparatus for generating transmission localoscillation signals and reception local oscillation signals in a mobileterminal, comprising: a first phase locked loop (PLL) block configuredto for generate a transmission local oscillation signal; a second PLLblock for generating a reception local oscillation signal; and acontroller configured to control the first PLL block to operate before aminimum time period required for the first PLL block to lock up from thestart point of a transmission burst period, and to control the secondPLL block to operate before a minimum time period required for thesecond PLL block to lock up from the start point of a reception burstperiod.
 2. An apparatus for generating a transmission local oscillationsignal and a reception local oscillation signal in a mobile terminal,comprising: a first PLL block configured to generate the transmissionlocal oscillation signal; a second PLL block configured to generate thereception local oscillation signal; and a controller for controlling thefirst PLL block to operate before an end point of a reception burstperiod and controlling the second PLL block to operate before an endpoint of a transmission burst period.
 3. A method of generating atransmission local oscillation signal and a reception local oscillationsignal in a mobile terminal having a first PLL block for generating thetransmission local oscillation signal and a second PLL block forgenerating the reception local oscillation signal, comprising:controlling the first PLL block to operate before a minimum time periodrequired for the first PLL block to lock up from the start point of atransmission burst period; and controlling the second PLL block tooperate before a minimum time period required for the second PLL blockto lock up from the start point of a reception burst period.
 4. Themethod of claim 3, further comprising: applying the reception localoscillation signal generated from the second PLL block to a radioreceiver for the reception burst period; and applying the transmissionlocal oscillation signal generated from the first PLL block to the radioreceiver for the transmission burst period.
 5. A method of generating atransmission local oscillation signal and a reception local oscillationsignal in a mobile terminal having a first PLL block for generating thetransmission local oscillation signal and a second PLL block forgenerating the reception local oscillation signal, the methodcomprising: controlling the first PLL block to operate before the endpoint of a reception burst period; and controlling the second PLL blockto operate before the end point of a transmission burst period.
 6. Themethod of claim 5, further comprising: applying the reception localoscillation signal generated from the second PLL block to a radioreceiver for the reception burst period; and applying the transmissionlocal oscillation signal generated from the first PLL block to a radioreceiver for the transmission burst period.